It has long been desired to maximize fuel economy and power in diesel engines while enhancing acceleration and preventing knocking and hesitation. Diesel fuel must ignite spontaneously and quickly (within 1 to 2 milliseconds) without a spark. The time lag between the initiation of injection and the initiation of combustion is called ignition delay. In high-speed diesel engines, a fuel with a long ignition delay tends to produce rough operation and knocking.
Two major factors affect ignition delay: the mechanical conditions in the engine and the chemistry of the fuel. The mechanical component is influenced by such factors as compression ratio, motion of the air charge during ignition and ability of the fuel injector to atomize fuel. The chemical component of ignition delay is influenced by such factors as the fuel's autoignition temperature, specific heat, density, viscosity, and other properties. The ability of a diesel fuel to ignite quickly after injection into a cylinder is known as its cetane number.
To minimize ignition delay in a diesel engine, it is desirable to enhance the mechanical component by maintaining the fuel injector's ability to precisely atomize fuel by keeping the injectors clean. However, this must be done in such a way that does not negatively affect the chemical component.
It would be beneficial to provide dispersant compositions that are highly effective in minimizing injector deposits in diesel engines, as well as intake valve deposits in gasoline engines, and that provide such an advantage without harm to the engine and without deterioration in engine performance.
Accordingly, one of the objects of the present invention is to provide a diesel fuel that provides effective detergency without attendant deterioration in engine performance.
Problems associated with fuel lubricity arose in the mid-1960's when a number of aviation fuel pump failures occurred. After considerable research, it was realized that advances in the refining of aviation turbine fuel had resulted in the almost complete removal of the naturally occurring lubricating components from the fuel. The removal of these natural lubricants resulted in the seizure of fuel pump parts. By the mid-1980's, it seemed likely that a similar problem was imminent in diesel fuel pumps. Fuel injection pump pressures had been steadily increasing while there was also a growing concern to reduce the sulfur content of the diesel fuel. The desire to reduce the sulfur content of the diesel fuel, in an effort to reduce pollution, required the use of more rigorous fuel refining processes. It was determined that as refining processes became more stringent, the naturally occurring sulfur, nitrogen and oxygen containing compounds and polyaromatics which contribute to diesel fuel's inherent lubricity were reduced or eliminated. In response to these developments, a number of effective lubricity additives were developed for diesel fuels. These additives are now widely used to enhance the lubricity of highly refined, low sulfur diesel fuels.
In certain types of in-line diesel injection pumps, engine oil contacts diesel fuel. Engine oil may also come into contact with the diesel fuel through direct addition of used engine oil to the fuel. Certain types of lubricity additives used in low sulfur diesel fuel have been found to contribute to fuel filter blockage and to pump plunger sticking. Lubricity additives having poor compatibility with engine oil have been shown to cause these problems. Compatibility is defined as the tendency for the diesel fuel containing the lubricity additive not to form fuel insoluble deposits, gels or heavy sticky residues when in contact with engine oil. These deposits, gels or residues have been shown to cause fuel filter blockage and injection pump sticking. The additives of the present invention are compatible with engine oil.
Gasoline fuels are also becoming subject to compositional constraints, including restrictions on sulfur content, in an effort to reduce pollutants. The principal concern is the effect of sulfur on exhaust catalyst life and performance. The lubricity requirements of gasoline are somewhat lower than for diesel fuel since the majority of gasoline fuel injection systems inject fuel upstream of the inlet valves and thus operate at much lower pressures than diesel fuel pumps. However, as automobile manufacturers desire to have electrically powered fuel pumps within the fuel tanks, failure of the pumps can be expensive to repair. These problems are also likely to increase as injection systems become more sophisticated and the gasoline fuels become more highly refined.
Additional pump wear concerns have arisen with the introduction of vehicles having direct injection gasoline (DIG) engines since the fuel pumps for these vehicles operate at significantly higher pressures than traditional gasoline fuel pumps.
Another area subject to pump wear and failure is the use of submerged fuel pumps in gasoline or diesel fuel storage tanks. It is important to reduce the wear of these submerged pumps due to the difficulty of accessing these pumps for repair and maintenance.
Many commercially available gasoline fuels contain gasoline detergents such as polyisobutylene amine and polyether amine. These compounds are known to have a minor effect on the wear properties of the fuel. A growing number of commercially available gasoline fuels contain oxygenates, such as methyltertiarybutylether (MTBE). These oxygenates are known to increase rates of wear of fuel pump components as they have very high friction coefficients. In light of the desire for more highly refined fuels, lower sulfur content and oxygenation of the fuels, there is presently a need for lubricity improvers for hydrocarbon fuels in order to obtain acceptable fuel pump life. The present invention addresses these problems by adding the novel Mannich reaction products to the fuel.
While the prior art is replete with numerous treatments for fuels, it does not disclose the addition of the present additives to hydrocarbon fuels or teach their use for providing enhanced detergency and lubricity to said fuels.